1. Field of the Invention
The invention generally relates to a structure of an output stage, in particular, to a structure of an output stage capable of advancing the driving capacity for the high output current thereof.
2. Description of Related Art
Nowadays, an operational amplifier is usually applied in diverse circuits, for example, an operational amplifier is operated on the amplification of signals, or is used to drive loads such as capacitance loads, or is implemented as a feedback circuit, or etc. Hence, an operational amplifier usually has characteristics of high input impedance, high loop gain, low output impedance, low common mode gain, and high gain bandwidth for applying in any kind of circuits. Especially, it is important for an operational amplifier to operate with high driving capacity under a high current condition.
The driving capacity of an operational amplifier can be advanced by enlarging the width of an output stage of the operational amplifier. In addition, although the output stage of the operational amplifier is usually protected e.g. by an over current protect (OCP) and an over temperature protect (OTP) to limit the current of the output stage thereof, the protection circuits described above sometimes fail. Therefore, it is still necessary to optimize an operational amplifier for operating under a high current condition.